This invention relates to an image reading device which includes a plurality of image sensors arranged in a widthwise direction of a document so as to scan sequentially from one lateral end to the other lateral end in the widthwise direction to read a document image, and outputs read data to such apparatus as image forming apparatus.
Conventionally, in an image reading device for use in an image forming apparatus such as a facsimile machine, there is arranged in a widthwise direction of a document an image sensor including a photoelectric conversion element array in which photoelectric conversion elements such as photodiodes are arranged in line. The image reading device reads a document image by causing the image sensor to scan in the widthwise direction (hereinafter referred to as a main scanning) and by moving the image sensor or document relatively to scan in a lengthwise direction of the document (hereinafter referred to as a sub-scanning). Since there is a limit in the number of photoelectric conversion elements mounted on a single image sensor, the number of photosensors and the length of the image sensor become insufficient in the case where the document width is large. Thus, in this case, a plurality of image sensors are arranged side by side according to the document size so as to scan in the same direction and synchronously to read the document image.
In this way, the array of photoelectric conversion elements sequentially scan so as to read the document image. Accordingly, there is a time difference between a reading timing of the first photoelectric conversion element and that of the last one. On the other hand, as described above, the image sensor and the document are moved relatively in the lengthwise direction of the document while the photoelectric conversion element array is being scanned. Consequently, an image data will have a discontinuity at a portion corresponding to a boundary between the juxtaposed image sensors. For example, in the case where a straight line S on a document G is read by image sensors 1 to 4 as shown in FIG. 10, the output data of the straight line S becomes discontinuous due to a difference in scanning time between two successively operated image sensors. Consequently, as shown in FIG. 10, an image reproduced is not accurately reproduced. Also, the appearance of the reproduced image is deteriorated.
As a measure against this problem, there has been proposed an image reading device in which adjacent image sensors are arranged such that main scanning directions thereof are alternately opposite to each other so as to correspond the reading timings at boundaries between two successively operated image sensors, to thereby eliminate the aforementioned discontinuity in the output data from the image reading device (Japanese Unexamined Patent Publication No. 2-202265).
However, since the main scanning directions of adjacent image sensors are alternately opposite to each other in the image reading device disclosed in the above publication, wires are connected to one end of the respective image sensors alternately at opposite positions, thereby complicating the wiring. Further, when the reading tracks of the respective image sensors are connected, the reproduced image is bent, thereby deteriorating the reproducibility and appearance. In order to solve this bending of the image, it is disclosed to arrange and incline the image sensors by the inclination of the reading tracks of the respective image sensors. However, this necessitates adjustment of the inclination of the respective image sensors, thus costing time and labor. Also, an adjusting operation requires skills since the inclination is adjusted by an extremely fine angle.
In addition, the above image reading device including a plurality of image sensors adopts a fabricating method of connecting manually the respective image sensors to one another and fixing the connected image sensors on a long rectangular substrate with adhesive or the like. Thus, there have been cases where the image sensors are fixed while being slightly displaced in the lengthwise direction of the document at the points of connection.
The displacement between the image sensors turns out to be a displacement of the image at the connections between the image sensors in the case where image data are output from the image sensors.